I'm trying to record video to mpeg. What bitrate to I use to record a 90 minute to 2 hour video so it fits on a 700mb cd?

I used to be able to record in avi using virtualdub with no problems. Now when I try to record in avi format no matter what the program I use my machine drops twice as many frames as it records. Any ideas? I have no such problem with mpeg.

Thanks